I don't understand, can you level up the VL by ONLY using the blood drain power? Someone said you can feed and powerbite as well? I'm going through stormcloak camps (sided with imperials) to level up, but it's going so slow. I only need about 4 more perks to max out the tree.

Using a power attack on an enemy that's almost dead lets your VL power bite and yes, it levels up the perk tree.

Do melee kills also level up the perk tree?

Not regular melee kills, just the power bite finisher.

Note you can also use the Life Drain on non-human creatures. Falmer, Deer, Saber Cats, Skeevers all add to the perk progression.

Yeah, I brutally murder horses at the camps and any passing wildlife bystanders lol. Does the progression remain the same or does it increase more for stronger beings, etc?

I'm pretty sure it's the same.

Oh alright thanks. I just got the Amulet of Bats from a Radiant Quest that has the bats from the perk tree absorb life, do you know if kills from that helps progression as well?